1. Field of the Invention
The present invention relates to a brake control device for a vehicle.
2. Description of the Related Art
Conventionally, there is known a brake apparatus including a master cylinder for generating a basic hydraulic pressure (master-cylinder hydraulic pressure) in accordance with an operation of a brake pedal that is performed by a driver of a vehicle, a hydraulic pump for generating a pressure difference generation hydraulic pressure for generating a pressure difference (linear-valve pressure difference) to be added to the basic hydraulic pressure, a pressure control valve (normally-open linear solenoid valve) for adjusting the pressure difference by using the pressure difference generation hydraulic pressure, and a friction brake mechanism for applying, to a wheel cylinder, a wheel-cylinder hydraulic pressure obtained by adding the pressure difference to the basic hydraulic pressure to generate a friction braking force in accordance with the wheel-cylinder hydraulic pressure (see Japanese Patent Application Laid-open No. 2007-276500).
In the brake apparatus described in Japanese Patent Application Laid-open No. 2007-276500, in order to reduce a load of linear solenoid valves, the wheel-cylinder hydraulic pressure is limited to a “minimum necessary hydraulic pressure to maintain a vehicle in a stopped state on a hill” while the vehicle is in a stopped state.
Moreover, for the brake apparatus described above, there is also known a technology for stopping the driving of the hydraulic pumps when a state of the vehicle transits from a moving state to a stopped state by depressing the brake pedal (see Japanese Patent Application Laid-open No. 2006-21745). With this technology, the durability of the hydraulic pumps can be ensured.
The following case is hereinafter considered. Specifically, the driving of the hydraulic pumps is stopped based on the stop of the vehicle by depressing the brake pedal (by an increase in braking torque) while the brake pedal is currently being operated. In this case, although the brake pedal is currently being operated, there may occur an event in which the vehicle starts moving by an operation of returning the brake pedal (by a decrease in braking torque). In this case, a configuration, which starts driving the hydraulic pumps based on the determination that “the vehicle has started moving (the state of the vehicle has transited from the stopped state to the moving state)”, is conceivable. However, the configuration described above brings about the following problem.
Specifically, when the driving of the hydraulic pumps is started, there may inevitably occur a phenomenon in which the amount of operation of the brake pedal slightly increases (hereinafter referred to as “brake pedal retraction phenomenon”) due to a temporary decrease in the amount of working fluid in a reservoir of the master cylinder. Therefore, in the configuration described above, the “brake pedal retraction phenomenon” occurs during the operation of returning the brake pedal (or immediately after the end of the operation of returning the brake pedal). In other words, a direction of movement of the brake pedal, which is caused by the “brake pedal retraction phenomenon”, becomes opposite to that of the brake pedal based on the operation of the brake pedal that is performed by the driver. As a result, there arises a problem in that the driver is undesirably susceptible to discomfort resulting from the operation of the brake pedal.